1. Field of the Invention
The present invention relates to a time division duplexing (TDD) transmission/reception apparatus and method, and more particularly, to a TDD transmission/reception apparatus and method which can enhance the efficiency of transmission/signal reception path isolation by polarizing transmitted signals and received signals with the aid of a polarized duplexer having an inclined surface such that the directivity of the transmitted signals is perpendicular to the directivity of the received signals.
2. Description of the Related Art
Time division duplexing (TDD) transmission/reception apparatuses use the same frequency band to transmit and receive signals. TDD transmission/reception apparatuses time-divide the transmission/reception of signals and downlink signals to an access point (i.e., a TDD base station) for a predetermined time period and then uplink signals from the access point for another predetermined time period.
In the case of using the same frequency band to transmit and receive signals as mentioned above, part of transmission power may be reflected by an antenna port and thus be infiltrated into a signal reception path of a reception system regardless of how perfectly the impedance of an antenna matches the impedance of a transmission/reception apparatus, thus resulting in a high signal reception path gain. A high signal reception path gain may considerably damage the reception system and adversely affect the reception sensitivity of the reception system, thereby lowering the reception capabilities of the transmission/reception apparatus. In addition, noise signals generated by a transmitter during the reception of received signals may interfere with the received signals, thereby lowering the reception capabilities of the transmission/reception apparatus.
Therefore, TDD transmission/reception apparatuses need an apparatus and method for minimizing the possibility of transmitted signals interfering with received signals by isolating a signal reception path from a signal transmission path.
FIG. 1 is a block diagram of a conventional TDD transmission/reception apparatus having radio frequency (RF) switches 150 and 155 for isolating a signal transmission path from a signal reception path. Referring to FIG. 1, the TDD transmission/reception apparatus includes a transmitter 100, a receiver 105, a high power amplifier (HPA) 110, a circulator 115, a band pass filter (BPF) 120, an antenna 125, and a synchronization signal generator 185. The transmitter 100 includes a modulator 130, an up converter 135, an RF amplifier 140, a step attenuator 145, and the RF switch 150. The receiver 105 includes a demodulator 180, a down converter 170, a step attenuator 165, a low noise amplifier 160, and the RF switch 155.
FIGS. 2A and 2B illustrate examples of the format of a frame of the conventional TDD transmission/reception apparatus illustrated in FIG. 1. Referring to FIGS. 2A and 2B, an uplink and a downlink are conducted at different times. In detail, referring to FIG. 2A, an uplink and a downlink are conducted with an uplink-downlink ratio of 16:6. Referring to FIG. 2B, an uplink and a downlink are conducted with an uplink-downlink ratio of 13:9. The synchronization signal generator 185 generates synchronization signals which turn on or off the RF switches 150 and 155 in response to the synchronization with an uplink with a downlink at a uniform interval TTG. The RF switch 150 in the transmitter 100 is turned on in response to a synchronization signal generated by the synchronization signal generator 185 and is turned off during a downlink period. On the other hand, the RF switch 155 in the receiver 105 is turned off during an uplink period and is turned on during the downlink period. A signal transmission path and a signal reception path can be isolated from each other by controlling the turning on or off of the RF switches 150 and 155.
The operation of the conventional TDD transmission/reception apparatus using the RF switches 150 and 155 will now be described in detail. The modulator 130 generates a transmitted signal to be transmitted, and the up converter 135 up-converts the frequency of the transmitted signal such that the transmitted signal can be readily transmitted. The RF amplifier 140 amplifies the transmitted signal, and the step attenuator 145 attenuates the power of the transmitted signal in steps. Thereafter, the transmitted signal is input to the HPA 110 only for an uplink period, and the HPA 110 amplifies the transmitted signal so that the transmitted signal has a very high power, and outputs the amplified result.
The RF switch 155 in the receiver 105 receives a received signal received via the antenna 125 from the circulator 115 only for a downlink period, and outputs the received signal to the LNA 160. The LNA 160 amplifies the received signal while minimizing noise. The step attenuator 165 attenuates the power of the received signal in steps, and the down converter 170 down-converts the frequency of the received signal. The demodulator 180 demodulates the received signal output by the down converter 170, thereby restoring desired source data.
The antenna 125 amplifies a transmitted signal. Then, the antenna 125 emits the amplified result to the air and receives a received signal from the air. The BFP 120 filters a transmitted signal and a received signal to a frequency band used by the conventional TDD transmission/reception apparatus, and the circulator 115 transmits a transmitted signal output by the HPA 110 to the BPF 120 and transmits a received signal received via the antenna 125 to the receiver 105.
As described above, in a case where a conventional TDD transmission/reception apparatus isolates a signal transmission path from a signal reception path using RF switches, a frame synchronization signal of a transmitted signal and a received signal must be extracted to control the RF switches, and then the RF switches must be turned on or off in response to the extracted frame synchronization signal while keeping monitoring the extracted frame synchronization signal. Thus, the structure of the conventional TDD transmission/reception apparatus may become too much sophisticated. In addition, since there is a need to realize a synchronization signal extraction algorithm, the manufacturing cost of the conventional TDD transmission/reception apparatus may increase.
Conventionally, as indicated in Table 1 below, the switching time of RF switches must be controlled within several dozens of usec, and thus, a high precision switching control technique is required. In addition, the control of the RF switches must be performed at intervals of 5 msec, and thus, a high precision switching control technique which can ensure a high durability against a considerable number of switching control repetitions is required. Repetitive RF switch controls, however, deteriorate the performance of RF switches over time, and eventually reduce the lifetime of transmission/reception apparatuses considerably.
TABLE 1VariablesValuesChannel Bandwidth10 MHzSampling Frequency (Fs)10 MHzSampling Interval (1/Fs)100 nsecFFT Size (NFFT)1024Quantity of Sub-Carriers Used864Quantity of Data Sub-Carriers768Quantity of Pilot Sub-Carriers96Sub-Carrier Frequency Interval9.765625 KHzValid Symbol Time (Tb = 1/Δ f)102.4 μsCP Time (Tg = Tb/8)12.8 μsOFDMA Symbol Time (Ts = Tb + Tg)115.2 μsTDD Frame Length5 ms